Microwave duplexer



Dgc. 23, 1958 J. F. ZALESKI 2,866,165

MICROWAVE DUPLEXER Filed Aug. 5, 1955 2 Sheets-Sheet 1 I GATE Gm RECEIVER m sa ' Ha Hz 51) INVEN TOR. JOHN F. ZAL ESKl ATTORNE Y.

Dec. 23, 1958 J. F. ZALESKI 2,366,165

MICROWAVE DUPLEXER Filed Aug. 5, 1955 2 Sheets-Sheet 2 gal 5 I GATE.

1N VEN TOR. JOHN F. ZALESKI ATTORNE).

MIQROWAVE DUPLEXER John F. Zaleslri, Valhalla, N. Y., assignor to General Precision Laboratory Incorporated, a corporation of New York Application August 5, 1955, Serial No. 526,738

Claims. (Cl. 333-6) This invention relates to microwave duplexing devices employing a plurality of gyromagnetic field rotators.

Pulsed microwave devices such as radar systems which radiate and receive microwave energy frequently employ a single antenna and/ or waveguide system for both transmitted and received pulses. It then becomes necessary to isolate the receiver to prevent reception of energy directly from the transmitter and it is preferable to isolate the transmitter so that received or locally generated energy does not enter it. This mutual isolation is at least partly secured by the conventional use of transmit-receive (TR) and anti-transmit-receive (ATR) switches or boxes. These devices usually consist of a combination of a short vapor discharge gap and a resonant chamber, and are fired by the incidence of transmitter power. They behave as switches operated by the presence or absence of transmitter power transmitted through them or resonated into them. Therefore one inherent requirement of such devices is that microwave energy of at least a prescribed minimum be applied to them to cause them to operate.

The duplexer of the present invention is distinguished from TR/ATR duplexers by its ability to operate with transmitters of power too low to operate TR or ATR devices. This ability comes about by the use of switch elements of the so-called gyro-rotator types which are switched from one to the other of their states by a direct-current or low-frequency control coil circuit, and not by microwave energy. These switch elements are in most cases arranged so that neither the transmitted nor the received microwave energy is carried by them, but such energy is switched or cut off by the operation of stubs or side arms which are changed from an effective length of x /4 to A /Z, or vice versa, by the switch element operation, K being wavelength in guide.

These gyro-rotator elements thus reflect widely different impedances to the associated guide system, thus serving as impedance-changing switches having no moving parts, actuated by a signal wire circuit, and in most cases not themselves carrying the microwave energy which is switched.

By gyro rotator is meant a device for rotating the direction of polarization of a guided noncircular microwave field, that is, a device which rotates the magnetic field therein in the Faraday magneto-optical sense. A simple example described in Patent No. 2,644,930, of C. H. Luhrs, dated July 7, 1953, consists of a round microwave guide containing a ferrite element and provided with means for impressing a magnetic field on the ferrite element. Microwave energy transmitted through the guide in the TE mode is rotated when the ferrite element is magnetized.

The instant invention employs two gyro rotators of this or any other type, suitably formed, enclosed and terminated as will be described hereinafter, in duplex circuits of the general form employed with TR and ATR tubes. It is preferable to employ two gyro rotators in such circuits to secure increased isolation and to control separately the two functions of isolating the receiver and isolating hired States Patent 0 2,866,165 Patented Dec. 23, 1958 the transmitter. Furthermore, the instant invention has the advantage that two or more gyro rotators can be used in taudem'in each of the two circuit positions to increase the isolation indefinitely, something that is inherently impossible when using TR and ATR tubes.

A preferable form of gyro rotator for use inthe instant invention comprises a round or square hollow guide containing an axial ferrite rod or tube and surrounded by a coaxial magnetizing coil. One end of the guide is closed by a metal disc and the other end is left open for attachmentto a rectangular hollow microwave guide as a series or shunt stub arm. Such a gyro rotator is distinguished by having only one point of connection and may be termed a one-terminal device.

A second preferable form of gyro rotator consists of a round or square hollow guide having both ends conductively closed. An axial ferrite rod or tube is secured to one end plate within the guide and a magnetizing coil is provided. A rectangular guide is joined to the device at the end supporting the rod in such a way as to excite the TE mode in the guide. The other end plate is provided with a coaxial output rectangular guide so oriented as to be coupled to the aforementioned TE field. When this gyro rotator is energized to rotate the microwave field by the output guide is completely decoupled and the device behaves as a single-terminal device.

Both types of gyro rotators are particularly advantageous in presenting widely different impedances to their attached input guides in the excited and unexcited states.

A further understanding of this invention may be secured from the detailed description and drawings, in which:

Figure 1 depicts a microwave duplexer containing two gyro rotators.

Figure 2 illustrates the wave forms existing in the circuit of Fig. 1.

Figures 3 and 4 illustrate modifications of portions of the circuit of Fig. 1.

Figure 5 illustrates'a modified form of gyro rotator and associated waveguides.

Figure 6 is ,a schematic circuit employing the gyro rotator of Fig. 5.

A common example of a microwave guide system in which transmitted and received pulses are guided through the same path, that, which is operated duplex, is a radar system in which one path leads from the transmitter through a guide to the radiator and the other path leads from the same radiator back through the same guide to the receiver. Thus the radiator constitutes a common terminal of the two guide systems of the transmitter and the receiver. Such a system is depicted in Fig. 1. The transmitting path is constituted by that from a magnetron transmitter 11 through a rectangular hollow guide 12 and 12 to a space radiator consisting of a horn 13 but which alternatively may be of any other type.

Reflected energy received by the same horn 13 is forced to take the path through the rectangular guide 12' and the side arm 14 to the crystal detector 16, from which the demodulated signal is conducted through conductor 17 to receiver 18. Received energy is prevented from reaching the magnetron 11, where it would be wasted and where it might disturb the constancy of the generated frequency,

by a gyro rotator 19. Transmitted energy is prevented from reaching the crystal demodulator 16 or receiver 18, where it might cause burnout or paralysis, by a second gyro rotator 21.

A conventional pulser 22 is connected through high potential conductors 23 to the magnetron 11, to which it supplies pulses of high potential. These pulses are also coupled by capacitor 24 to a gate generator 26 which may be, for example, a monostable multivibrator, which generates low-voltage pulses in synchronism with the high-voltage pulses. These low-voltage pulses are applied to an electromagnetic relay 27 having a contact arm 28 and front and back contacts 29 and 31. Front contact 29 is connected through conductor 32 to coil 33 of gyro rotator 19 and contact 31 is connected through conductor 34 to coil 36 of gyro rotator 21.

In the pulsing of magnetron 11 the applied pulses are conventionally negative and are depicted in Fig. 2, graph A. The synchronous output pulses of the gate circuit 26 are depicted in Fig. 2, B, as positive and having a length suitable for operating relay 27. The front contact potential pulses are similar to the coil pulses B and the back contact pulses are depicted by graph C. Obviously pulses such as those .of graphs B and C can as well be secured directly from an appropriate electronic gate generator, and for pulse repetition frequencies higher than canbe handled by an electromagnetic relay it is necessary to do so. Such a circuit is indicated in Fig. 3, both coils 33 and 36 being energized directly from the gate generator 26.

Gyro rotator 19, Fig. 1, comprises a round microwave guide 37 secured to the upper broad face 38 of rectangular guide 12. The lower end of round guide 37 is open so that guides 12 and 37 are coupled and constitute a rectangular/round transition. This transition is preferably impedance-matched, as is customary. The upper end of the gyro rotator is closed by a conductive metal plate 39. A coaxial rod 41 is supported by end plate 39 and extends through part or all of the length of the guide 37. This rod 41 is a gyromagnetic element, and it may assumeother forms and have other disposltions, as indicated in the patent of Luhrs supra. The internal length L of guide 37 is made equal to onequarter of the microwavelength in guide, or A /4. This length may of course'be any odd multiple of one quarter wavelength, or

in which N is .any positive integer or zero.

In the operation of the gyro rotator 19 its behavior is that of a short-circulated series guide arm. When unenergized, the fact that it is a quarter-wave long causes it to nterpose high impedance amounting to an open circuit 1n guide 12. When, however, coil 33 is excited the microwave field entering the arm is rotated both before and after reflection from the end plate 39, so that the arm behaves as if it were one-half wavelength long and presents very low impedance to guide 12. Microwave energy passing through guide 12 therefore ignores guide 37 and passes toward the right as if guide 19 had been removed and the guide side 38 contained no opening.

The gyro rotator 21 is exactly like gyro rotator 19, being provided with-an actuating coil 36 and containing .a ferrite axial rod. Its length R is made electrically equal to A /4, coil 36 being unenergized. Whencoil 36 is .energized the gyro rotator behaves as if its length were A 2.

The distance M between gyro rotator 21 and the rectangular guide face 38 is MM, and the demodulator 16 is positioned and arranged beyond the gyro rotator 21 as to absorb and demodulate all microwave energy which reaches it.

In the operation of the device depicted in Fig. 1, when magnetron 11 is pulsed, microwave energy is transmitted toward the .right in guide 12. Simultaneously the gate generator 26 is energized, energizing relay 27 which attracts it armature 28, making contact with its front contact 29 and energizing gyro rotator coil 33. The gyro rotator 19 behaves as if it were one-half wavelength long, producing an effect of continuity in guide 12 so that the microwave energy contained therein passes toward the right. Gyro rotator 21 being unenergized,"the conductivity of its end plate 42 is reflected to guide 12 so that the generated microwave energy is transmitted to the right in guide 12, ignoring the side arm 14. Any energy leaking into arm 14 meets an open circuit at rotator 21 serving as a quarter-wave short-circuited stub, further protecting demodulator 16. The microwave energy passes through guide 12 and is coupled to space or radiated by horn 13.

Reflected or other microwave energy impinging on horn 13 is transmitted toward the left in guide 12. When this occurs after the termination of the transmitting pulse or during any interpulse period P, Fig. 2, graph A, relay 27 is in the deenergized state and its contact arm 28 is in contact with back contact 31, deenergizing coil 33 and energizing coil 36. The gyro rotator 21 then behaves as if its length were 1 /2, presenting a low impedance to energy entering arm 14 as though the rotator were not present. The impedance seen from guide 12' is therefore that of demodulator 16, and the received energy in guide -12' enters-guide 14. This energy ignores the gyro rotator 21 and passes it, since the gyro rotator reflects continuity to guide arm 14, and the energy impinges upon demodulator 16 and is demodulated. The dimension Q between side arm 14 and gyro rotator 19 is made and since gyro rotator '19 is deenergized it interposes an open circuit or high impedance in guide 12. The distance Q, being an odd multiple of a quarter wavelength makes this open circuit appear like a short circuit or low impedance across guide 12 at the junction of arms 12 and '14, so that no received energy is lost by passage to the left in guide 12. Additionally, the open circuit or high impedance -in guide 12 imposed by gyro rotator 19 at the junction of guide 12 and gyro rotator 19 further prevents the loss of energy into the magnetron and both actions protect the magnetron 11 from effects of this energy.

If desired the gyro rotator 21 may be made to have an internal length R of A /Z and by making its rotational effect such that when energized it behaves as if its length were 41 its action is reversed and the gating circuit may 'be simplified by connecting both coils 33 and 36 to contact 29. I

When electromagnetic gating is employed a circuit such as illustrated in Fig. 4 may be utilized. In this case the length of rotator 21 is made equal to x /2 and the coil 36 is energized during the transmitting pulse, so that guide 12 behaves as'ifcontinuous' and an open circuit is interposed in arm 14. When-received energy is applied from guide 12 to side arm 14, coil 36 is deenergized and the opening of the side arm is receptive to the received energy. The opening of gyro rotator 21 in the side arm wall, being one-half wavelength from the metal end plate 42, does not obstruct passage of the received energy to the demodulator 16.

Figure 5 illustrates a modified form of gyro rotator and its association with a rectangular guide 12 which may be used in place of the gyro rotator 21, Fig. l, and associated waveguides. The energizing circuit of Fig. 1 except as modified by Fig. 4 is employed with the gyro rotator of Fig. 5.

The gyro rotator contains a round microwave guide 43 having ends closed by metal plates 44 and 46. A ferrite rod or tube 47 is coaxially positioned in the round guide and passes through the end plate 46, in which it is secured. An energizing coil 48 surrounds rod 47 outside guide 43 orthogonally at or near the inner surface of rod 47 projecting inside the guide. The end 49 of the rod 47 is tapered, or terminates in a tapered piece of dielectric material to eliminate the microwave impedance discontinuity which would otherwise be caused by the squared end of rod 47. A rectangular guide 51 constituting a shunt side arm of guide 12 opens into the round guide 43 orthogonally at or near the inner surface of end plate 46 to serve as one terminal of the gyro rotator,

so that when microwave energy'is applied at this terminal the TE mode is excited in guide 43. A second rectangular guide 52 is centrally and orthogonally secured in and to end plate 44 at such orientation as to be coupled to the TB field excited by guide 51 in the absence of any field rotation. Guide 52 is terminated in a demodulator 16 connected to receiver 18. 7

One advantage of this construction is that the lower end of ferrite rod 47 secured to end plate 46 in eflect does not constitute an impedance discontinuity, and it has been found to be very easy to impedance-match the transition constituted by the junction of guides 51 and 43 with great accuracy over a broad band.

This gyro rotator is distinctive in that its internal length S need not be any particular multiple of onequarter wavelength in guide and, in fact, may have any value desired. However, this dimension in combination with the parameters of the field-rotating components are under the resistriction that when the gyro rotator is excited the single-trip rotation of a microwave field in travelling the length S must be exactly 90".

In the operation of the gyro rotator of Fig. 5 the circuit of Fig. 6 is employed. Energy from magnetron 11 is pulsed into guide 12 and rotators 19 and 43 are both energized. Rotator 19 reflects low series impedance to the guide as before described and the transmitting energy passes it and, tending to enter shunt side arm 51, Figs. 5 and 6, is rotated in round guide 43 by exactly 90 so that it cannot enter the receiver arm 52 but is reflected from end 44. The length S of round guide 43 and the length T of shunt arm 51 are so chosen as to present low series impedance to the transmitting energy, which therefore passes on through guide 12 and is radiated by horn 13.

The dimension S, as stated, is such that the rotational effect during one-way passage of the field is 90". The energy reflected then meets energy applied from arm 51 in phase, so that when the length T of arm 51 equals onehalf wavelength in guide low series impedance is reflected to the main guide 12.

Energy received by horn 13 from space is impressed from guide 12' on shunt side arm guide 51 and from it on round guide 43. Since coil 48 is deenergized at this time, the field within guide 43 is not rotated and passes out guide 52, where it is demodulated in demodulator 16, the demodulated energy being received in receiver 18. As before described in connection with Fig. 1, gyro rotator '19 interposes an open circuit to isolate magnetron 11 and reflects a short circuit toward gyro rotator 43.

What is claimed is:

1. A microwave duplexer comprising, a microwave guide having an input terminal and a load terminal, microwave transmitter means connected to said input terminal for ex citing a polarized field mode in said guide, a first gyro rotator constituting a short-circuited side arm of said guide adjacent said input terminal, said gyro rotator reflecting impedance interdicting said guide in one condition of excitation and reflecting impedance permitting guide conductivity in another condition of excitation, a microwave branch guide connected to said guide to constitute an orthogonal side arm, said branch guide being positioned between said first gyro rotator and said load terminal, a receiving demodulator means connected to said branch guide, and a second gyro rotator contained in said orthogonal side arm, said second gyro rotator reflecting impedance interdicting said branch guide in one condition of excitation to prevent microwave energy from entering from said guide and removing said interdiction in another condition of excitation to allow microwave energy to enter said branch guide from said guide.

2. A microwave duplexer providing mutual isolation between a transmitter and a receiver connected to a common terminal comprising, a microwave guide connecting said transmitter and said common terminal, a first gyro rotator constituting a short-circuited side arm connected to said guide, said short-circuited side arm having a length equal to an odd multiple of one-quarter wavelength in guide when said gyro rotator is deenergized but having an apparent length of any multiple of one-half wavelength in guide when the gyrorotator is energized by magnetization thereof, a microwave side arm guide connecting said receiver to said guide between said first gyro rotator and said common terminal and a second gyro rotator associated with said side arm guide, said second gyro rotator effectively disabling said side arm guide or enabling it to convey microwave energy in accordance with the condition of energization or deenergization of the second gyro rotator.

3. A microwave duplexer for a pulsed transmitter comprising, a main waveguide having an input terminal adapted to be connected to said pulsed transmitter and a load terminal, a branch waveguide orthogonally joined to said main waveguide, means for coupling a receiver to said branch waveguide, a first closed end symmetrical cross section waveguide section joined to said main waveguide at a point intermediate said input terminal and the junction of said branch waveguide with said main waveguide, said firs t waveguide section including means for rotating microwave energy in the Faraday magneto-optical sense under the influence of a magnetic field, a second closed end symmetrical cross section waveguide section joined to said branch waveguide at a point intermediate the junction of said branch waveguide with said main waveguide and the means coupling said receiver to said branch waveguide, said second waveguide including means for rotating microwave energy in the Faraday magneto-optical sense under the influence of a magnetic field, and means for applying magnetic fields to said first and second waveguide sections in timed relation with the generation of pulses by said pulsed transmitter whereby said first and second waveguide sections alternately reflect short circuits at their junctions with their respective waveguides.

4. A microwave duplexer for a pulsed transmitter comprising, a main waveguide having an input terminal adapted to be connected to said pulsed transmitter and a load terminal, a branch waveguide orthogonally joined to said main waveguide, means for coupling a receiver to said branch waveguide, a first waveguide section symmetrical in cross section joined to said main waveguide at a point intermediate said input terminal and the junction of said branch waveguide with said main waveguide, said first waveguide section having a closed end positioned an odd integral number of quarter Wavelengths in the guide from the junction of said first waveguide section with said main guide, means positioned in said first waveguide section for rotating microwave energy in the Faraday magneto-optical sense under the influence of a magnetic field, a second waveguide section symmetrical in cross section joined to said branch waveguide at a point intermediate the junction of said branch Waveguide with said main waveguide and said receiver coupling means, said second waveguide section having a closed end positioned an odd integral number of quarter wavelengths in the guide from the junction of said second waveguide section with said branch waveguide, means positioned in said second waveguide section for rotating microwave energy in the Faraday magneto-optical sense under the influence of a magnetic field, and means for alternately and selectively applying magnetic fields to the respective microwave rotating means in said first and second waveguide sections of such intensity as to produce a virtual electrical length between said closed ends and the junctions of said first and second waveguide sections with their respective waveguides of an integral number of half wavelengths.

5. A microwave duplexer for a pulsed transmitter comprising, a main waveguide having an input terminal adapted to be connected to said pulsed transmitter and a load terminal, a branch waveguide orthogonally joined to said main waveguide, means for coupling a receiver to said branch waveguide, a first waveguide stub symmetric'altin crossesectionjoined to said'niain waveguide intermediate: said input terminal and the junction ofsaid branch-waveguide with said main waveguide, said first waveguide stub having. a-closed-end an odd number of quarter wave lengths in-theguide from said main waveguide; means positionedinsaid first waveguide stub for rotating microwave energy in the Faraday magnetooptical sense under the influenceof a magnetic field, a second waveguide stub symmetrical in'cross section joined to said bran'ch waveguide at a point intermediate the junction ofsaid branch-waveguide with said -rnain waveguide and said receiver coupling means, said second waveguide stub having a closed end an integral number of half wavelengths in'the guide from said branch waveguide, means positioned in said second Waveguide stub for rotating microwave energy in the Faraday magnetooptical sense under the influence of a magnetic field, and means acting concomitantly with the production of a pulse by said transmitter for applying magnetic fields of such intensity'to the respective microwave rotating means of said first and second waveguide stubs as to render the virtual electrical length of said first Waveguide stub an integral'number: of half wavelengths and the virtual. electrical length of said' second waveguide stub an odd'numberof quarter wavelengths.

References Cited in the file of this patent UNITED STATES PATENTS 2,577,118 FiSke Dec. 4, 1951 2,584,901 Miller Feb. 5, 1952 2,594,732 Cork Apr. 29, 1952 2,606,248 Dicke Aug. 5, 1952 2,681,987 Farr June 22, 1954 2,719,274 Luhr Sept. 27, 1955 2,728,050 Van de Lindt Dec. 20, 1955 2,757,341' Lundstrom July 31, 1956 FOREIGN PATENTS 980,648 France Dec. 27, 1950 OTHER REFERENCES VanTrier: Experiments on the Faraday Rotation of Guide Waves, Applied Scientific Research, vol. 3, No. 2, July 27, 1953, pages 142-144. 

